NOTE: THIS DOCUMENT IS OBSOLETE, PLEASE CHECK THE NEW VERSION: "Mathematics of the Discrete Fourier Transform (DFT), with Audio Applications --- Second Edition", by Julius O. Smith III, W3K Publishing, 2007, ISBN 978-0-9745607-4-8. - Copyright © 2017-09-28 by Julius O. Smith III - Center for Computer Research in Music and Acoustics (CCRMA), Stanford University
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Signals as Vectors
For the DFT, all signals and spectra are length
. A length
sequence
can be denoted by
,
, where
may be real (
) or complex (
). We now wish to regard
as avector
6.1 in an
dimensional vector space. That is, each sample
is regarded as a coordinate in that space. A vector
is mathematically a single point in
-space represented by a list of coordinates
called an
-tuple. (The notation
means the same thing as
.) It can be interpreted geometrically as an arrow in
-space from the origin
to the point
.
We define the following as equivalent:
whereis the
th sample of the signal (vector)
. From now on, unless specifically mentioned otherwise, all signals are length
.
Subsections